Corneal astigmatism after penetrating keratoplasty is a major clinical problem, preventing 10% of these patients from attaining useful vision. The development of this astigmatism has been attributed to pre, intra, and post-operative causes. The main objective of this study is to model corneal surface changes after penetrating keratoplasty in adult cats, a species which has little pre-existing corneal astigmatism. Preoperative examinations will include biomicroscopy, intraocular pressure, pachometry and corneascopic photographs of all cat eyes. The right eyes of 10 cats will be the recipients of penetrating keratoplasties from 5 donor cats using accepted and standardized techniques. Diametric measurements of donor and recipient corneal buttons and positioning of donor corneal buttons will be taken. Examinations identical to preoperative will be performed on postoperative days 1, 4, 7, 14, 28, 42, 56, 70, 84, 98, 112, 142, 173, 186, 193, 200, 207, and 214. The corneal sutures will be removed at 6 months and the cats killed at 7 months after surgery. The model will be developed from digitized corneascopic data. Ring images will be described by indices including eccentricity, angularity, and latitudinal and longitudinal symmetry and rotation, to permit meaningful comparisons of preoperative corneal shape with each postoperative corneascopic measurement. For each postoperative day, pre-to-postoperative differences will be combined over all cats, and 48 graphs of recovery over time for each ring (8) for each index (6) produced. Correlations between postoperative corneal deviance and characteristics of donor and recipient buttons, donor/ recipient fit, changes in fellow eyes and clinical measurements will be tested for significance to suggest causal relationships. Preoperative corneascopic measurements will be compiled to describe the normal cat corneal surface. Because of the high success rate for corneal transplants, surgeons are now concerned with postoperative astigmatism. Our model describes the central and midperipheral cornea at any given time in the postoperative course and how corneal regions change over time. This will allow analysis of the factors which may prevent the development of a postoperative spherical cornea. Ultimately specific recommendations could lead to the minimization of postkeratoplasty astigmatism.